I also have a manual Drum Car and am also working on the brakes right now.
I am in the process of changing out all the lines to SS Disc lines.
Some observations.....
The Bracket that secures the front Brake Hose appears to be different on a Disc car than a drum car. When you get the Disc Lines, they will have bends in them that wont match up to your drum hose bracket, so you may have to bend them a bit. I did, and it wasnt hard.
Drum Car Bracket
Disc Car Bracket
The Ends of the Disc Brake Line Kit Will be different in some places than the Drum Line Kit. ie, the master cylinder lines will have different fittings. Depending on which proportional valve you use, you may need different fittings on the new lines. If you stick with Mustang specific parts, everything should work fine. If you go with an after market Proportional valve like I did, The ends will be different. If you go stainless, you do not want to be changing ends. So make sure you order the lines with the correct ends.
Conversion Kit.
I also like the SSBC Kit. It is inexpensive and will fit. I havnt got it yet, but its on my list.
https://www.npdlink.com/product/disc-brake-conversion-kit-street-bandit-front-drum/207115/200824
Master/Booster Upgrade.
If your kit doesnt come with the master and brake booster, you will need to get them.
I prefer the LEED Brakes 9" Booster. If you ask nicely when you order they will also send you the new Bolt on Pivot Point for the pedal.
https://leedbrakes.com/i-21155650-9-inch-power-brake-booster-black.html
You could also go with the master/booster combo.
https://leedbrakes.com/i-21155649-hydraulic-kit-power-brake-booster-kit-71-73-ford-mustang.html
You will need to remove the Drivers side Shock Tower Brace for access. Then Remove the Drum Master Cylinder and disconnect from pedal, and brake switch. (Giant pain in the ass, remove the seat first.)
This will leave you with 2 Studs holding the Pedal Assembly in place. Remove the 2 Studs by threading on a nut, then a 2nd nut and lock them into each other, then turn the inside nut to rotate the stud bolt out.
Once the pedal assembly is out You can remove the pedal from the bracket. If you can, this would be a good time to blast and paint/powder coat all that stuff.
Then using a drill press, drill the hole for the new bolt in pivot point. Since the rod on the booster is lower than the drum master, it must be relocated.
You can bolt it on, or bolt it and weld it in place.
While everything is out, replace all your lines. This will be immeasurable fun! You will need to unbolt the Emissions canister and preferably the vacuum canister to get access to the passenger side lines and union.
Use these Reference pictures as a guide.
Then Put back together and mount the booster and pedal assembly.
Mount the Master Cylinder AFTER Bench Bleeding. Install the lines pointing up so they wont leak fluid and loose prime on the master.
Connect it all up and bleed it. it will be lots easier to bleed the disc brakes than the drums were.